The disclosure relates to an emergency adjustment device for blade pitch adjustment systems for wind energy installations.
Wind energy installations, which produce electrical energy from the wind, have rotors with variable-pitch blades. The angle of the rotor blades governs the area on which the wind acts, thus making it possible to adjust the power of the wind energy installation. The angle is substantially dependent on the wind speed. When a limiting speed is reached, the blades are set such that the wind acts on a small an area as possible. The aim of this is to prevent the wind power machine from being damaged. The position in which the wind has no area to act on is referred to as the feathered position.
It is possible for the adjustment of the rotor blades which is carried out during normal operation no longer to be feasible in the event of a defect in the adjustment device, caused, for example, by a component failure after a lightning strike. The wind energy installation can in consequence reach an unacceptable high rotor rotation speed, which could result in destruction of the wind energy installation. It is therefore particularly important to ensure that the rotor blades are moved safely to the feathered position in the event of a failure such as this. This is referred to as so-called emergency adjustment.
In the case of wind energy installations, it is important for the wind energy installation not to be damaged in the event of failure of the supply system. The closed-loop control which is used to adjust the rotor blade angles during normal operation no longer operates if the supply system fails.
DE 103 35 575B4 discloses an emergency operating device in which voltage for the electric motor for adjustment of the rotor blades is made available by a converter. The converter contains a rectifier, an intermediate circuit and an inverter connected in series. An energy store is provided in the intermediate circuit, and ensures the power supply for the electric motor in the event of a power supply system failure. However, one problem in this case is that the converter electronics are at risk of failure. This is particularly the case if the power supply system failure has been caused by a lightning strike on the wind energy installation, since the voltage increase caused by the lightning can damage the electronics.
The object of the disclosure is to provide an adjustment device for rotor blades of a wind energy installation, with the adjustment device being less susceptible to defects than the adjustment devices known from the prior art.
This object is achieved by the subject matter of the independent claim. Advantageous developments are specified in the dependent claims.
According to the disclosure, an adjustment device is provided for rotor blades of a wind energy installation, in which an alternating-current motor is provided for adjusting the angular position of the rotor blades. An input is used for receiving an input alternating current. A frequency converter is provided for producing a second alternating current at a second frequency, with the second alternating current driving the alternating-current motor. Furthermore, a DC voltage source and an inverter are provided for converting the voltage provided by the DC voltage source to an alternating current for the alternating-current motor. In this case, the inverter is separate from the frequency converter.
Since the inverter is provided separately from the frequency converter, particularly robust components can be used for the inverter. A microcontroller is preferably used for the frequency converter, since microcontrollers allow high energy efficiency, but are susceptible to defects, since microcontrollers are in the form of an integrated circuit. Only a small number of components need be provided for the inverter, thus decreasing the failure rates and increasing the reliability. It is also possible that the failure rates of these components can be calculated using conventional means.
For so-called alternating-current adjustment systems, adjustment systems with polyphase machines, preferably in the form of asynchronous motors, the present disclosure offers an equivalent reversionary level to conventional direct-current adjustment systems, adjustment systems using direct-current machines, preferably in the form of compound motors.
When using direct-current machines in the adjustment device of a wind energy installation, it is feasible for the energy stores in the uninterruptable power supply to be connected directly with the aid of a switch, allowing the rotor blades to be moved to the safe feathered position in this way.
However, at present, this solution is impossible for conventional alternating-current adjustment systems, since a polyphase motor cannot be operated directly with direct current. The present disclosure makes it possible to convert the DC voltage provided from the energy stores in the uninterruptable power supply, to be precise to a three-phase AC voltage allowing a polyphase motor to be operated.
In the case of direct-current adjustment systems, starting torques which occur can be reduced only by additional circuitry measures, for example a starting resistance in series with the armature winding. Because of the high ratings and the physical spaces, these starting resistances generally have to be fitted outside the switchgear cabinet. The duration of use of the starting resistances is controlled by timing relays, partially in redundant form. Because of the additional components and the wiring complexity, the system becomes more expensive, reducing the reliability.
The inverter preferably consists of discrete components, in order to make the inverter as robust as possible.
If the output signal from the inverter is at a fixed frequency, the alternating-current motor can be operated at a frequency at which it produces a high torque.
In one embodiment, the energy store is in the form of a capacitor. An energy store such as this can be made particularly robust, with the capability to store sufficient energy, as well, with the aid of double-layer capacitors.
In another embodiment, the energy store is in the form of a rechargeable battery. This can be charged at regular intervals during normal operation, in order that it can provide sufficient electrical power to swivel the rotor blades to the feathered position in the event of an emergency off.
In one embodiment, the alternating-current motor is in the form of a polyphase motor, and the inverter is designed for producing a polyphase current. This allows a conventional asynchronous machine or synchronous machine to be used as the alternating-current motor, with the inverter providing a current as is also produced by the frequency converter.
In the worst case, when an emergency adjustment is made to the feathered position, a load reversal can occur at the motor, particularly in the case of large wind energy installations, caused by an excessively high wind load or because of the gravitational forces on the falling blade. In this case, the motor operates as a generator. In order to prevent reactions, caused by generator voltage spikes, on the energy stores in the uninterruptable power supply, the excess energy must be dissipated by means of a suitable protection circuit.
The present disclosure operates with voltage measurement at the inputs of the connection to the energy stores. If the voltage is at a critical level, a discharge circuit is activated cyclically until the voltage has reached a safe level.
If the inverter has overvoltage protection on its direct-current side, excess voltage occurring during generator operation of the electric motor can be dissipated. This prevents the DC voltage source, for example the capacitor or rechargeable battery, from being destroyed by overvoltage.
In one embodiment, the inverter has a multiplicity of switches which are each provided between a node on the DC voltage side and a node on the AC voltage side. Each of the switches is controlled by a pulse-width-modulated signal. Such pulse-width-modulated signals can be produced by discrete components.
In a further embodiment, the control signals for the switches are produced by an apparatus which has an operational amplifier which, at its inputs, receives output signals from a sine-wave signal generator and a triangular-waveform generator.
A movement rate window should be complied with when moving to the feathered position in an emergency. In the case of direct-current adjustment systems, this can be achieved only with a high level of complexity, since the rotation speed of direct-current motors depends on the voltage of the energy stores in the uninterruptable power supply. In one embodiment, in addition to movement rate which can be set to be fixed, the disclosure also allows a ramp function during starting and braking. The ramp function is in general activated during starting and selectively during braking, by means of a switching contact, shortly before the feathered position is reached. This measure minimizes torque surges on components and structures throughout the entire wind energy installation.
The disclosure also relates to a wind energy installation having an adjustment device according to the invention. A wind energy installation such as this is distinguished by a high safety level during emergency disconnection.
The wind energy installation preferably contains a motor brake for the alternating-current motor. This allows the alternating-current motor to be stopped, for example in the event of a defect in the adjustment device.